1. Field of the Invention
The invention relates to a power supply system and, more particularly, to a system that supplies electric power from a power supply coil, provided at a facility, to a power receiving coil, provided for a mobile unit such as a vehicle, in a non-contact manner and a method of controlling the system.
2. Description of the Related Art
There is known a non-contact power supply system that uses electromagnetic induction. For example, Japanese Patent Application Publication No. 2006-345588 (JP-A-2006-345588) describes a non-contact power supply device and a power supply system for an autonomous mobile unit. The non-contact power supply device described in JP-A-2006-345588 includes a primary coil that is electromagnetically coupled to a secondary coil of the autonomous mobile unit; communication means that acquires a power receiving state of the secondary coil side; power supply state acquisition means that acquires a power supply state of the primary coil side; power supply efficiency acquisition means that acquires a power supply efficiency from the power supply state of the primary coil side acquired by the power supply state acquisition means and the power receiving state of the secondary coil side acquired by the communication means; positioning means that moves a position of the primary coil so as to maximize the power supply efficiency acquired by the power supply efficiency acquisition means; retry instruction means that transmits a retry signal to the secondary coil side through the communication means when the power supply efficiency is lower than or equal to a predetermined value; and control means that controls the above means of the non-contact power supply device.
Supply of electric power in a non-contact manner is not limited to supplying electric power between the primary coil and the secondary coil as described above; instead, supply of electric power in a non-contact manner may also include supplying electric power using resonance coils. Supply of electric power in a non-contact manner using resonance coils is configured so that a power supply-side resonance coil and a power receiving-side resonance coil are provided between the primary coil (power supply coil) and the secondary coil (power receiving coil) and then electric power is supplied between the pair of resonance coils. In other words, the power supply coil and the power supply-side resonance coil are provided as a primary-side coil, and the power receiving coil and the power receiving-side resonance coil are provided as a secondary-side coil. The power supply coil, the resonance coils and the power receiving coil are electromagnetically coupled to one another, and electric power from the power supply coil is supplied to the power receiving coil through the resonance coils. In supplying electric power using the resonance coils as described above, a distance between the primary coil (power supply coil) and the power supply-side resonance coil and a distance between the secondary coil (power receiving coil) and the power receiving-side resonance coil are fixed. When a distance between the resonance coils changes, the power supply efficiency may also vary. In addition, when a battery mounted on a mobile unit such as a vehicle is charged as well, charging efficiency may possibly decrease.